Cavitation refers to the process of forming vapor bubbles in a liquid. This can be done in a number of manners, such as through the use of a swiftly moving solid body (as an impeller), hydrodynamically, or by high-frequency sound waves.
Apparatuses and methods for producing cavitation are described in U.S. Pat. Nos. 3,399,031; 4,675,194; 5,026,167; 5,492,654; 5,810,052; 5,837,272; 5,931,771; 5,937,906; 5,969,207; 5,971,601; 6,365,555 B1; 6,502,979 B1; 6,802,639 B2; 6,857,774 B2; 7,041,144 B2; 7,178,975 B2; 7,207,712 B2; 7,247,244 B2; 7,314,516 B2; and 7,338,551 B2. One particular apparatus for producing hydrodynamic cavitation is known as a liquid whistle. Liquid whistles are described in Chapter 12 “Techniques of Emulsification” of a book entitled Emulsions—Theory and Practice, 3rd Ed., Paul Becher, American Chemical Society and Oxford University Press, NY, N.Y., 2001. An example of a liquid whistle is a SONOLATOR® high pressure homogenizer, which is manufactured by Sonic Corp. of Stratford, Conn., U.S.A. The liquid whistle directs liquid under pressure through an orifice into a chamber having a knife-like blade therein. The liquid is directed at the blade, and the action of the liquid on the blade causes the blade to vibrate at audible or ultrasonic frequencies. Hydrodynamic cavitation is produced in the liquid in the chamber downstream of the orifice.
Liquid whistles have been in use for many years, and have been used as in-line systems, single or multi-feed, to instantly create fine, uniform and stable emulsions, dispersions, and blends in the chemical, personal care, pharmaceutical, and food and beverage industries.
It has been found, however, that improvements to such devices may be desirable. In particular, some of such devices need to be more easily cleanable, especially when they are used for processing products with microbial sensitivity (subject to growth of microbes) such as food products, cosmetics, and pharmaceuticals. For example, although the SONOLATOR® high pressure homogenizer is available in “clean-in-place” models, such a feature is only available on very simple models which have no mechanism for adjusting the spacing of the blade relative to the orifice.
In addition, at least some of these devices are not scalable for some transformations. For example, in some cases where a pilot-size unit is used prior to “scaling up” to a production-size unit for commercial production, the physical properties (such as stability, viscosity, appearance, and micro-structure) of the finished product produced by the production-sized unit may be quite different from those of the product produced by the pilot-size unit, even under the same operating conditions. As used herein, the term “operating conditions” refers to conditions such as: pressure drop, back pressure, temperature of liquid components fed into the apparatus, and the distance between the blade and the orifice. The search for improved apparatuses and methods for mixing by producing shear and/or cavitation, and components for such apparatuses has, therefore, continued.